A novel unbalanced translocation between chromosomes 5p and 18q leading to dysmorphology and global developmental delay

Background: Individuals with various sized terminal duplications of chromosome 5p or terminal deletions of chromosome 18q have been described. These aberrations may cause congenital malformations and intellectual disability of varying severity.

Methods: Via an international collaborative effort, we obtained a cytogenetic diagnosis for a 5-year-old boy of Afro-Caribbean ancestry who has global developmental delay, dysmorphology, hypotonia, feeding difficulties, bilateral club feet, and intellectual disability.

Results: Conventional G-banded karyotyping showed additional chromatin of unknown origin on the long arm of chromosome 18. SNP microarray confirmed the loss of ~6.4 Mb from chromosome 18q: arr[hg19] 18q22.3-q23(71,518,518-77,943,115)x1. The source of the additional chromatin was determined from the microarray to be ~32 Mb from the short arm of chromosome 5 (arr[hg19] 5p13.3-p15.33(51,045-32,062,984)x3). The unbalanced translocation was verified by fluorescent in situ hybridization (FISH). Both parents are healthy and have normal karyotypes suggesting that this abnormality arose de novo in the proband, although gonadal mosaicism in a parent cannot be excluded.

Conclusion: The combination of clinical features in this individual is most likely due to the partial deletion of 18q and partial duplication of 5p, which to our knowledge has not been previously described.